The present invention is directed to a package comprising a semirigid material, for example, corrugated cardboard, wherein said package is provided at the top with at least two horizontal copings which form a support surface for another package when a number of the packages are stacked.
Patent GB-A-2,057,398 teaches a packing comprising a bottom on which fold lines articulate two transverse sidewalls and two longitudinal side walls prolonged at their ends by wing pieces that line the transverse walls and thus reinforce the stacking strength of the packing and, two horizontal copings articulated by fold lines along the upper edges of the longitudinal walls extending parallel to the bottom toward the interior of the tray.
It is obvious that when such a packing is made of corrugated cardboard it cannot be used to pack wet commodities or ones that sweat heavily, such as fresh fish, meat products and fresh fruits and vegetables.
French Pat. No. 1,515,445 and U.S. Pat. No. 3,866,816 both describe a means of water-proofing the interior of a cardboard packing in the form of a boat, said means consisting of a protective film of thermoplastic material extending with no discontinuity over the inner faces of the packing, which is adhered to the latter by application of heat or by means of a thermoplastic binder. To produce such a package, the original sheet of cardboard is placed in a mold with its side walls erect, and the film of thermoplastic material is introduced in the heated state by suction or blowing on the inside of the ready-mounted cardboard sheet. The film is then adhered onto the sheet.
It is the aim of the present invention to embody a protection of this type for a package provided with inwardly foldable flaps or flange members. The package is characterized in that it comprises a lining constituted by a film of thermoplastic material that is applied by thermal molding against the inner faces of the bottom and of the side walls and which, without discontinuity, extends against the under face of the inwardly folded flange member and is folded over the free inner edge thereof to apply against the upper face of the flange member.
Any thermoplastic film can be used within the scope of the invention. Note, however, that if the film is semirigid, for example of the polystyrene type, it is not necessary to adhere it to the cardboard walls because the lining is self-locking inside the cardboard packing. As a matter of fact, if an attempt is made to extract the entire lining from the packing, by pulling, for example, on the flanges of the lining covering the upper face of the inwardly folded flange member, the latter will counteract this withdrawal by the fact that the lining has an inner cross section larger than that of the opening defined between the flange members on the opposite end of the package.
But, if the thermoplastic film is flexible and easy to crush, it must be adhered to the walls of the cardboard packing. With this in mind, it is possible either to use a plastic film, one face of which has an adhesive agent that is reactivated when the film is heated to permit its thermal molding, or to imprint on the inner surface of the cardboard, zones of adhesive coating that are reactivated at the time of the thermal molding.
It is also possible to reinforce the integration between the lining and the cardboard packing by forming apertures in the flange members through which the portions of film situated on the opposite faces of the flange members become welded together during the thermal molding.
The thermoplastic material of the film must be of food grade so it will not alter the tase of the foods packed therein. The thickness of the film can be comprised between 100 and 500 .mu.m.
According to another characteristic of the invention, the strips of film covering the outer faces of the flange members and the thicknesses of the other walls of the packing extend beyond the outside of the latter to form a peripheral flange on which a cap of thermoplastic material can be heat-sealed to insure that the package is perfectly sealed with respect to the ambient medium.
In another embodiment of the invention, the cardboard packing is also protected by an outer lining of thermoplastic material having the form of a shell applied against the outer faces of the bottom and the side walls of the packing and terminating at its upper edge in a peripheral flange parallel to the bottom and projecting laterally outward, the peripheral portion of the inner lining that covers the outer faces of the flange members and the upper edges of the other walls of the packing also extending outside beyond the latter to form a projecting peripheral flange, the said flanges of the outer shell and of the inner lining being heat-sealed together.
By reason of its double external and internal protection, the packing is impermeable both with respect to the commodities it contains and to outside agents.